Lab focus questions -- echinoderm/frog/chicken development lab Flashcards
echinoderm development:
what is the difference b/n an oocyte and an egg?
an oocyte becomes an egg when meiosis is complete
echinoderm development:
what is the difference b/n an egg and a zygote?
an egg becomes a zygote when fertilization is complete (that is, when the haploid sperm and egg nuclei fuse to become 1 diploid nucleus)
echinoderm development:
what indication is there that the sea urchin egg has an animal-vegetal polarity?
polar – 2 ends that are not identical
sea urchin eggs show polarity
top – animal hemisphere
bottom – vegetal hemisphere
structures that develop from animal hemisphere are different than structures that develop from vegetal hemisphere
difference probably based on differences in info stored in the cytoplasm of the animal and vegetal hemispheres
one easily observable indication of polarity in sea urchin eggs – nucleus is offset towards the animal pole
echinoderm development:
what are the biochemical consequences of egg activation?
rates of RNA and protein synthesis increase dramatically
DNA is synthesized in anticipation of cell division
echinoderm development:
what must happen to restore the diploid condition during fertilization?
the haploid egg and sperm nuclei must fuse to become the diploid zygote nucleus
echinoderm development:
what is polyspermy?
polyspermy is the fertilization of an egg by more than 1 sperm cell
echinoderm development:
what problem does polyspermy present?
w/ more than 2 sets of chromosomes (1 from sperm and 1 from egg nucleus) –> there can be abnormal development
echinoderm development:
what minimizes chance for polyspermy?
2 basic mechanisms to prevent polyspermy –
a fast polyspermy block – electrical
a slower polyspermy block (lifting off of the fertilization membrane)
echinoderm development:
what is meant by holoblastic cleavage?
holoblastic cleavage – vertical cleavage furrows completely cut thru the egg from animal to vegetal pole
echinoderm development:
what is the sequence of division plane orientation in early holoblastic cleavage?
first 2 cleavages are vertical and perpendicular to each other
3rd cleavage is horizontal
echinoderm development:
what constitutes the ectoderm, the endoderm, and the mesoderm of the sea urchin embryo?
ectoderm – outer cell layer of gastrula
endoderm – archenteron (primitive gut)
mesoderm – consists of:
- primary mesenchyme cells that migrate into the blastocoel from the basal plate of the blastula as gastrulation begins (which form the skeleton)
- secondary mesenchyme cells that migrate from the invaginating archenteron (which form muscle cells)
development lab focus questions:
what are some indicators of animal-vegetal polarity in eggs?
sea urchins – nucleus is offset toward the animal pole
amphibians –
- nucleus is offset toward the animal pole
- more dense yolk in the vegetal hemisphere than in the animal hemisphere
- there is pigment on the surface of the animal hemisphere
chickens –
- nucleus is offset toward the animal pole
- there is very dense yolk in the vegetal hemisphere
development lab focus questions:
what is the effect of yolk on early development?
yolk affects cleavage
amphibians – yolk retards cleavage as it proceeds toward the vegetal pole
2nd cleavage begins in the animal hemisphere before the first is complete in the vegetal half
3rd (horizontal) cleavage is closer to the animal than to the vegetal pole (perhaps where there is less resistance to the formation of a cleavage furrow) –> yields animal blastomeres that are smaller than the vegetal blastomeres
later cleavage is more rapid in the animal hemisphere than in the vegetal, so that animal hemisphere blastomeres continue to be smaller than vegetal blastomeres
chickens – there is a very large amount of yolk in eggs – so much that only a very small portion of the cell at the animal pole, the blastodisc, is free enough from yolk to have any cleavage occur in it at all
development lab focus questions:
how does cleavage in echinoderms, amphibians, and birds compare?
echinoderms – cleavage is holoblastic
amphibians – cleavage is holoblastic, but slow at the vegetal pole
chickens – cleavage is restricted to the animal pole. Cleavage of the chick zygote is quite different from that in echinoderms and amphibians. The first several cleavages are vertical, and extend only a very short distance downward; horizontal cleavages eventually occur, which give rise to several layers of blastomeres the make up a disc of cells situated on top of the mass of yolk below
development lab focus questions:
how does the formation of the blastula in echinoderms, amphibians, and birds compare?
echinoderms – the wall of the blastula is 1-cell thick all around; blastocoel forms so that it occupies the animal and vegetal hemispheres essentially equally
amphibians – floor of the blastocoel is considerably thicker than the roof of the blastocoel. the blastocoel forms essentially exclusively in the animal hemisphere of the blastula
birds – the blastocoel is a very narrow space underlying the blastodisc, sitting on an enormous amount of yolk
frog/chicken development:
echinoderms develop from eggs that have ___ yolk
very little
frog/chicken development:
amphibians develop from eggs that have ___ yolk
a moderate amount of
frog/chicken development:
birds develop from eggs that have ___ yolk
huge amounts of yolk
frog/chicken development:
amount of yolk in an egg influences considerably the way….
early development progresses, particularly w/ respect to cleavage patterns and to morphogenesis
development lab focus questions:
how does gastrulation in echinoderms, amphibians, and birds compare?
echinoderm gastrulation – like the classic pushing the leaky tennis ball – an invagination from the vegetal pole into the blastocoel
amphibian gastrulation – an involution of cells just ventral to where the gray crescent was located in the zygote – this inward movement continues as cells of the animal hemisphere migrate down over the larger yolky cells of the vegetal hemisphere
bird gastrulation – 2 steps:
1) lower layer of blastodisc cells migrates away – form a layer of hypoblast cells below the epiblast (which the remaining cells fo the blastodisc are now known as)
2) as hypoblast expands, the epiblast cells migrate rearwards and medially to form the primitive streak, thru which streak cells migrate to form the mesoblast, a layer of cell b/n the epiblast and the hypoblast
development lab focus questions:
what are some derivatives of ectoderm, mesoderm, and endoderm in amphibians and birds?
ectoderm – epidermis of the skin, hair, nails, lens, cornea, entire nervous system; lining of the nose and mouth
mesoderm – muscle, bone, cartilage, notochord, blood, kidneys, gonads
endoderm – lining of esophagus, stomach, intestine; lungs, liver, pancreas, thyroid, parathyroids, bladder lining
what are indicator(s) of animal-vegetal polarity in eggs?
distribution of pigment in the egg
distribution of yolk in the egg
location of the nucleus in the egg
how does cleavage differ b/n frog zygotes and chicken zygotes?
frogs – cleavage occurs throughout the cytoplasm of frog zygotes, both in animal and vegetal hemispheres
chickens – cleavage is restricted to the animal hemisphere
the large amount of yolk in the vegetal hemisphere of a chicken egg prevents cleavage there, so cleavage is restricted to the animal pole
which of the following do the blastulas of the sea urchin, frog, and chicken embryos hold in common?
presence of a cavity called the blastocoel
the blastocoel is a distinctive feature of the blastula
which of the following is/are true of polyspermy?
polyspermy may occur if the fertilization membrane fails to form
fertilization membranes lifts off surface of egg after first sperm makes contact. But while forming, electrical block protects just-fertilized egg
what types of zygotes show holoblastic cleavage?
what types of zygotes don’t show holoblastic cleavage?
yes:
mammal zygotes
amphibian zygotes
echinoderm zygotes
no: chicken zygotes (only very small portion of cell at animal pole -- blastodisc -- is free enough from yolk to have any cleavage occur in it at all)
cleavage in early mammalian embryos is most like the cleavage in which of the following?
early echinoderm embryos
echinoderm eggs have little yolk in them, like mammalian eggs. The amount of yolk in the egg can determine cleavage patterns.
which of the following is true of the first three cleavages in echinoderm development?
the first 2 cleavages are vertical, the 3rd is horizontal
what occurs during sea urchin development?
formation of mouth from archenteron
formation of anus from blastopore
archenteron developing from an inward buckling of the vegetal plate
formation of a fertilization membrane
